First close-ups of Pluto thrill scientists

Mankind's first close-up look at Pluto did not disappoint on Wednesday: The pictures showed ice mountains on Pluto about as high as the Rockies and chasms on its largest moon, Charon, that appear six times deeper than the Grand Canyon.

Especially astonishing to scientists was the total absence of impact craters in a zoom-in shot of one otherwise rugged slice of Pluto. That suggests that Pluto is not the dead ice ball many people think, but is instead geologically active even now, its surface sculpted not by collisions with cosmic debris but by its internal heat, the scientific team reported.

Breathtaking in their clarity, the long-awaited images were unveiled in Laurel, Maryland, home to mission operations for NASA's New Horizons, the unmanned spacecraft that paid a history-making flyby visit to the dwarf planet on Tuesday after a journey of nearly 10 years and 4.8 billion kilometers.

"I don't think any one of us could have imagined that it was this good of a toy store," principal scientist Alan Stern said at a news conference. He marveled: "I think the whole system is amazing. ... The Pluto system is something wonderful."

As a tribute to Pluto's discoverer, Stern and his team named the bright heart-shaped area on the surface of Pluto the Tombaugh Reggio. US astronomer Clyde Tombaugh spied the frozen, faraway world on the edge of the solar system in 1930.

Thanks to New Horizons, scientists now know Pluto is a bit bigger than thought, with a diameter of 2,370 km, but still just two-thirds the size of Earth's moon. And it is most certainly not frozen in time.

The zoom-in of Pluto, showing an approximately 240-km swath of the dwarf planet, reveals a mountain range about 3,353 meters high and tens of kilometers wide. Scientists said the peaks - seemingly pushed up from Pluto's subterranean bed of ice - appeared to be a mere 100 million years old. Pluto itself is 4.5 billion years old.

"Who would have supposed that there were ice mountains?" project scientist Hal Weaver said. "It's just blowing my mind."

John Spencer, like Stern, a scientist at the Southwest Research Institute, called it "just astonishing" that the first close-up picture of Pluto didn't have a single impact crater. Stern said the findings suggesting a geologically active interior are going to "send a lot of geophysicists back to the drawing boards".